U.S. patent number 6,340,379 [Application Number 09/308,222] was granted by the patent office on 2002-01-22 for gas filter, method for producing a gas filter and use of said gas filter.
This patent grant is currently assigned to Creavis Gesellschaft fuer Technologie und Innovation mBH. Invention is credited to Gerhard Hoerpel, Christian Hying, Bernd Penth.
United States Patent |
6,340,379 |
Penth , et al. |
January 22, 2002 |
Gas filter, method for producing a gas filter and use of said gas
filter
Abstract
A gas filter, a process for producing a gas filter and the use
of the gas filter. The filtration of gases, in particular of gases
which are contaminated by solids, e.g. automobile exhaust gases, is
difficult since the solids which have been filtered out block the
filter over the course of time. The gas filter of the invention can
be used over relatively long periods of time since it is
regenerable. The improvement achieved by the invention compared to
conventional gas filters is that the filter comprises a composite
material which can be heated in a simple manner by application of a
voltage to the electrically conductive support material of the
composite material and thermally decomposable substances which can
block the filter can be decomposed. The filter of the invention can
be used wherever gases which are contaminated by thermally
decomposable solids have to be cleaned.
Inventors: |
Penth; Bernd (Lebach,
DE), Hoerpel; Gerhard (Nottuln, DE), Hying;
Christian (Rhede, DE) |
Assignee: |
Creavis Gesellschaft fuer
Technologie und Innovation mBH (Marl, DE)
|
Family
ID: |
27512604 |
Appl.
No.: |
09/308,222 |
Filed: |
July 26, 1999 |
PCT
Filed: |
September 18, 1998 |
PCT No.: |
PCT/EP98/05946 |
371
Date: |
July 26, 1999 |
102(e)
Date: |
July 26, 1999 |
PCT
Pub. No.: |
WO99/15257 |
PCT
Pub. Date: |
April 01, 1999 |
Foreign Application Priority Data
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|
|
|
|
Sep 20, 1997 [DE] |
|
|
197 41 498 |
Mar 18, 1998 [DE] |
|
|
198 11 708 |
Mar 19, 1998 [DE] |
|
|
198 12 035 |
May 8, 1998 [DE] |
|
|
198 20 580 |
Jun 3, 1998 [DE] |
|
|
198 24 666 |
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Current U.S.
Class: |
95/45; 210/490;
210/500.26; 264/45.1; 210/500.25; 427/372.2; 55/523; 96/11; 55/524;
428/307.7 |
Current CPC
Class: |
B01D
46/0056 (20130101); B01D 46/24 (20130101); B01D
46/4263 (20130101); B01D 46/48 (20130101); B01D
46/521 (20130101); B01D 53/228 (20130101); B01D
53/32 (20130101); B01D 53/8675 (20130101); B01D
53/885 (20130101); B01D 67/0041 (20130101); B01D
67/0048 (20130101); B01D 67/0069 (20130101); B01D
67/0072 (20130101); B01D 67/0093 (20130101); B01D
69/141 (20130101); B01D 71/02 (20130101); B01D
71/024 (20130101); B01D 71/028 (20130101); B01J
35/06 (20130101); B01J 37/0215 (20130101); B01J
37/0225 (20130101); B01J 37/033 (20130101); B01D
46/0068 (20130101); Y10T 428/249957 (20150401); B01D
2265/06 (20130101); B01D 2323/08 (20130101); B01D
2325/02 (20130101); Y10S 55/10 (20130101) |
Current International
Class: |
B01J
35/06 (20060101); B01J 37/00 (20060101); B01J
37/02 (20060101); B01J 37/03 (20060101); B01J
35/00 (20060101); B01D 46/48 (20060101); B01D
53/88 (20060101); B01D 46/24 (20060101); B01D
53/86 (20060101); B01D 53/22 (20060101); B01D
53/32 (20060101); B01D 71/00 (20060101); B01D
71/02 (20060101); B01D 059/12 (); B01D 071/02 ();
B01D 071/04 () |
Field of
Search: |
;210/500.25,500.26,490,505,508,510.1,650 ;264/45.1,44,46.4
;428/307.7 ;427/372.2 ;485/920 ;55/524,523 ;204/554 ;95/45
;96/11 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
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|
|
0263468 |
|
Oct 1987 |
|
EP |
|
0332789 |
|
Mar 1988 |
|
EP |
|
0426546 |
|
Oct 1990 |
|
EP |
|
0585152 |
|
Jul 1993 |
|
EP |
|
0778076 |
|
Nov 1996 |
|
EP |
|
96/00198 |
|
Jan 1998 |
|
WO |
|
Primary Examiner: Fortuna; Ana
Attorney, Agent or Firm: Oblon, Spivak, McClelland, Maier
& Neustadt, P.C.
Claims
What is claimed is:
1. A regenerable gas filter for filtering gases which comprises a
bendable and rollable composite material based on at least one
open-structured and material-permeable support and having on at
least one side of the support and in the interior of the support at
least one inorganic component consisting essentially of at least
one compound of a metal, a semimetal or a mixed metal and at least
one element of main groups III to VII, wherein the composite
material has a thickness of 5 to 150 .mu.m and can be bent to a
radius of down to 2 mm and wherein the composite material has pores
permeable to particles having maximum size of from 0.1 to 10 .mu.m
and wherein there is present in the composite material at least one
inorganic component as a particle size fraction having a particle
size of 1 to 250 nm.
2. A gas filter as claimed in claim 1, wherein the open-structured
and material-permeable support has intermediate spaces having a
size of from 0.02 to 500 .mu.m.
3. A gas filter as claimed in claim 1, wherein the support
comprises at least one material selected from the group consisting
of carbon, metals, alloys, glass, ceramics, minerals, plastics,
amorphous substances, natural products, or composite materials.
4. A gas filter as claimed in claim 1, wherein the support
comprises at least woven, felted or ceramically bound fibers or at
least sintered spheres or particles.
5. A gas filter as claimed in claim 1, wherein the support
comprises at least one at least partially electrically conductive
material.
6. A gas filter as claimed in claim 1, wherein the support is
perforated.
7. A gas filter as claimed in claim 1, wherein the
material-permeable support has been made material-permeable by
laser treatment or ion beam treatment.
8. A gas filter as claimed in claim 1, wherein the support
comprises fibers of at least one material selected from the group
consisting of carbon, metals, alloys, ceramics, glass, plastics,
composite materials, minerals, natural products and amorphous
substances or fibers of at least one combination of these
materials.
9. A gas filter as claimed in claim 1, wherein the support
comprises woven fibers of metal or alloys.
10. A gas filter as claimed in claim 1, wherein the support
comprises at least one woven steel mesh.
11. A gas filter as claimed in claim 1, wherein the support
comprises at least one woven mesh having a mesh opening of from 5
to 500 .mu.m.
12. A gas filter as claimed in claim 1, wherein the support
comprises at least one expanded metal having a mesh opening of from
5 to 500 .mu.m.
13. A gas filter as claimed in claim 1, wherein the support
comprises a i sintered metal, a sintered glass or a metal nonwoven
having a pore width of from 0.1 to 500 .mu.m.
14. A gas filter as claimed in claim 1, wherein the support
comprises at least aluminum, silicon, cobalt, manganese, zinc,
vanadium, molybdenum, indium, lead, bismuth, silver, gold, nickel,
copper, iron, titanium, platinum, stainless steel, steel or brass
or an alloy of these materials or a material coated with Au, Ag,
Pb, Ti, Ni, Cr, Pt, Pd, Rh, Ru and/or Ti.
15. A gas filter as claimed in claim 1, wherein the said inorganic
component consists essentially of at least one compound of the
transition elements and of main groups III to VII or at least one
compound of the transition elements and at least one compound of
main groups III to VII, with the compounds having a particle size
of from 0.01 to 25 .mu.m.
16. A gas filter as claimed in claim 1, wherein the said inorganic
component consists essentially of at least one compound of an
element of transition groups III to VIII or at least one element of
main groups III to V with the elements Te, Se, S, O, Sb, As, P, N,
Ge, Si, C, Ga, Al or B or at least one compound of an element of
transition groups III to VII and at least one element of main
groups III to V with at least one of the elements Te, Se, S, O, Sb,
As, P, N, Ge, Si, C, Ga, Al or B or a mixture of these
compounds.
17. A gas filter as claimed in claim 16, wherein the inorganic
component comprises at least one compound of the elements Sc, Y,
Ti, Zr, V, Cr, Mo, W, Mn, Fe, Co, B, Al, In, Tl, Si, Ge, Sn, Pb, Sb
or Bi and the elements Te, Se, S, O, Sb, As, P, N, C or Ga.
18. A gas filter as claimed in claim 1, wherein the inorganic
component comprises at least one compound selected from
aluminosilicates, aluminum phosphates, zeolites or partially
exchanged zeolites.
19. A gas filter as claimed in claim 1, wherein the inorganic
component comprises at least one compound selected from amorphous
microporous mixed oxides which may be admixed with up to 20% of
non-hydrolyzable organic compounds.
20. A gas filter as claimed in claim 1, wherein the inorganic
component comprises at least aluminum oxide or titanium oxide.
21. A gas filter as claimed in claim 1, wherein the composite
material comprises at least two particle size fractions of at least
one inorganic component.
22. A gas filter as claimed in claim 21, wherein the particle size
fractions in the composite material have a particle size ratio of
from 1:1 to 1:100.
23. A gas filter as claimed in claim 21, wherein the composite
material has a ratio of amounts of the particle size fractions of
from 0.01:1 to 1:0.01.
24. A gas filter as claimed in claim 23, wherein the composite
material comprises particle size fractions having an average
particle size of from 0.3 to 3 .mu.m.
25. A gas filter as claimed in claim 1, wherein the material
permeability of the composite material can be limited to particles
having a particular maximum size by means of the particle size of
the inorganic component used.
26. A gas filter as claimed in claim 1, wherein the composite
material has pores which are permeable to particles having a
maximum size of from 0.1 to 0.5 .mu.m.
27. A gas filter as claimed in claim 1, wherein the composite
material can be bent to a radius of down to 1 mm.
28. A gas filter as claimed in claim 1, wherein the gas filter has
the composite material rolled into a suitable container having at
least one gas inlet and at least one gas outlet, with the composite
material being arranged so that the gas to be filtered must, after
entering the gas filter, pass at least once through the composite
material before it can leave the gas filter via the gas outlet.
29. A gas filter as claim in claim 28, wherein thermally
decomposable solids or liquids which have been filtered from a
filtered gas and block the pores of the composite material are
removed from the gas filter by baking the gas filter by application
of a voltage to the support of the composite material.
30. A gas filter as claimed in claim 29, wherein the gas inlet and
the gas outlet are provided with a flow- or pressure-measuring
device by means of which the pressure or the amount of gas entering
and leaving the filter is measured and when a preset difference
between the measured values, which represents a measure of the
blocking of the composite material, is reached, the baking of the
gas filter is commenced.
31. A gas filter as claimed in claim 1, wherein the composite
material comprises at least one catalytically active component.
32. A gas filter as claim in claim 31, wherein thermally
decomposable solids or liquids which have been filtered from a
filtered gas and block the pores of the composite material are
removed from the gas filter by baking the gas filter by application
of a voltage to the support of the composite material.
33. A gas filter as claim in claim 32, wherein the gas inlet and
the gas outlet are provided with a flow-or pressure-measuring
device by means of which the pressure or the amount of gas entering
and leaving the filter is measured and when a preset difference
between the measured values, which represents a measure of the
blocking of the composite material, is reached, the baking of the
gas filter is commenced.
34. A gas filter as claimed in claim 31, wherein the composite
material comprises, as catalytically active component, at least one
oxide of at least one of the elements Mo, Sn, Zn, V, Mn, Fe, Co,
Ni, As, Sb, Pb, Bi, Ru, Re, Cr, W, Nb, Hf, La, Ce, Gd, Ga, In, Tl,
Ag, Cu, Li, K, Na, Be, Mg, Ca, Sr and Ba.
35. A gas filter as claimed in claim 31, wherein the composite
material comprises at least titanium suboxide as catalytically
active component.
36. A gas filter as claimed in claim 31, wherein the composite
material comprises, as catalytically active component, at least one
metal compound selected from among the compounds of the metals Pt,
Rh, Ru, Ir, Au, Ag, Os, Re, Cu, Ni, Pd and Co.
37. A gas filter as claimed in claim 31, wherein the composite
material comprises, as catalytically active component, at least one
metal selected from among the metals Pt, Rh, Ru, Ce, Ir, Au, Ag,
Os, Re, Cu, Ni, Pd and Co.
38. A process for producing a gas filter as claimed in claim 1,
which comprises producing a material-permeable composite material
by applying, in and on at least one open-structured and
material-permeable support, at least one suspension which comprises
at least one inorganic component comprising at least one compound
of at least one metal, a semimetal or a mixed metal with at least
one of the elements of main groups III to VII and a sol and by
solidifying the suspension on and in the support material by
subsequent heating at least once.
39. The process as claimed in claim 38, wherein the suspension is
applied on and in the support by printing, pressing-on,
pressing-in, rolling-on, doctor blade coating, painting-on,
dipping, spraying or casting.
40. The process as claimed in claim 38, wherein an open-structured
and material-permeable support comprising a material selected from
the group consisting of carbon, metals, minerals, ceramics,
composite materials or at least one combination of these materials
is used.
41. The process as claimed in claim 38, wherein the
support-comprises at least one material which is at least partially
electrically conductive.
42. The process as claimed in claims 38, wherein a woven stainless
steel mesh is used as support.
43. The process as claimed in claim 38, wherein the suspension
which comprises at least one inorganic component and at least one
metal oxide sol, at least one semimetal oxide so! or at least one
mixed metal oxide sol or a mixture of these sols is produced by
suspending at least one inorganic component in at least one of
these sols.
44. The process as claimed in claim 38, wherein the suspension
comprises at least one catalytically active component.
45. The process as claimed in claim 38, wherein the sols are
obtained by hydrolyzing at least one metal compound, a mixed metal
compound or at least one semimetal compound using a liquid, a gas
or a solid.
46. The process as claimed in claim 45, wherein the liquid, gas or
solid used for hydrolyzing the metal compound is water, water
vapor, ice, alcohol or an acid or a combination of these
compounds.
47. The process as claimed in claim 45, wherein the compound to be
hydrolyzed is added prior to the hydrolysis to alcohol or an acid
or a combination of these liquids.
48. The process as claimed in claim 45, wherein at least one metal
nitrate, a metal chloride, a metal carbonate, a metal alkoxide
compound or at least one semimetal alkoxide compound is
hydrolyzed.
49. The process as claimed in claim 48, wherein at least one metal
alkoxide compound or at least one semimetal alkoxide compound
selected from among the alkoxide compounds of the elements Ti, Zr,
Al, Si, Sn, Ce and Y or a metal nitrate, a metal chloride or a
metal carbonate selected from among the metal salts of the elements
Ti, Zr, Al, Si, Sn, Ce and Y is hydrolyzed.
50. The process as claimed in claim 49, wherein a titanium alkoxide
compound is hydrolyzed.
51. The process as claimed in claim 38, wherein the hydrolysis of
the compounds to be hydrolyzed is carried out using at least half
the molar ratio of water, based on the hydrolyzable group of the
hydrolyzable compound.
52. The process as claimed in claim 38, wherein the hydrolyzed
compound is treated with at least one organic or inorganic
acid.
53. The process as claimed in claim 52, wherein the organic or
inorganic acid has a concentration of from 10 to 60%.
54. The process as claimed in claim 52, wherein the hydrolyzed
compound is treated with at least one mineral acid selected from
the group consisting of nitric acid, sulfuric acid, perchloric acid
and hydrochloric acid or a combination of these acids.
55. The process as claimed in claim 38, wherein a titanium dioxide
sol acidified with mineral acid is used as sol.
56. The process as claimed in claim 38, wherein at least one
inorganic component having a particle size of from 1 to 10,000 nm
is suspended in a sol.
57. The process as claimed in claim 56, wherein an inorganic
component comprising at least one compound selected from among
metal compounds, semimetal compounds, mixed metal compounds and
metal mixed compounds with the elements of main groups III to VII,
or at least one mixture of these compounds, is suspended.
58. The process as claimed in claim 56, wherein an inorganic
component comprising at least one compound from among the oxides of
the transition elements or the elements of main groups III to V is
suspended.
59. The process as claimed in claim 58, wherein the oxides are
selected from among the oxides of the elements Sc, Y, Ti, Zr, V,
Nb, Cr, Mo, W, Mn, Fe, Co, B, Al, In, Ti, Si, Ge, Sn, Pb and
Bi.
60. The process as claimed in claim 38, wherein at least one
inorganic component used is aluminum oxide having a particle size
of from 0.3 to 3 .mu.m.
61. The process as claimed in claim 38, wherein at least one
catalytically active component is incorporated into the composite
material.
62. The process as claimed in claim 38, wherein at least one
catalytically active component is added to the sol.
63. The process as claimed in claim 62, wherein at least one
catalytically active component comprises at least one compound
selected from among metal compounds, semimetal compounds, mixed
metal compounds and metal mixed compounds with the elements of main
groups III to VII or organic compounds or at least one mixture of
these compounds.
64. The process as claimed in claim 38, wherein at least one
catalytically active component having a particle size of from 1 to
10,000 nm is suspended in a sol.
65. The process as claimed in claim 38, wherein at least one noble
metal, a noble metal compound or a zeolite is incorporated as
catalytic component into the composite material.
66. The process as claimed in claim 38, wherein at least one
catalytically active component comprises at least one compound
selected from the group consisting of zeolite, silicalite or
amorphous mixed oxide.
67. The process as claimed in claim 38, wherein the proportion by
mass of the suspended components corresponds to from 0.1 to 500
times the hydrolyzed compound used.
68. The process as claimed in claim 38, wherein the suspension
present on and in or else on or in the support is solidified by
heating the composite at least once at from 50 to 1000.degree.
C.
69. The process as claimed in claim 68, wherein the composite is
subjected to a temperature of from 50 to 100.degree. C. for from 10
minutes to 5 hours.
70. The process as claimed in claim 68, wherein the composite is
subjected to a temperature of from 100 to 800.degree. C. for from 1
second to 10 minutes.
71. The process as claimed in claim 68, wherein heating is carried
out by means of heated air, hot air, infrared radiation, microwave
radiation or electrically generated heat.
72. The process as claimed in claim 68, wherein heating is carried
out using the support material as electrical resistance heating
element.
73. The process as claimed in claim 38, wherein the solidification
of the suspension is achieved by applying the suspension on and in
a preheated support.
74. The process as claimed in claim 38, wherein at least one
support is unwound from a roll, passed at a speed of from 1 to 50
m/h through at least one apparatus which applies the suspension on
or in or on and in the support and at least one further apparatus
which makes possible the solidification of the suspension on or in
or on and in the support by heating and the composite material
produced in this way is wound up on a second roll.
75. The process as claimed in claim 38, wherein an unsintered
ceramic or inorganic layer is applied to a support and is
strengthened by heating.
76. The process as claimed in claim claim 38, wherein the dried and
strengthened composite material is impregnated with a solution
comprising at least one metal salt, the composite material which
has been treated in this way is dried by heating and the metal salt
which is present in and on or else in or on the composite material
is reduced to metal.
77. The process as claimed in claim 38, wherein a metal salt which
is present in the composite material is reduced to metal by
treating the composite material with a reducing agent.
78. The process as claimed in claim 77, wherein the reducing agent
used is a borohydride.
79. The process as claimed in claim 38, wherein a metal salt which
is present in or on or else in and on the composite material is
reduced to metal by using the composite material as electrode in an
electrolysis.
80. The process as claimed in claim 38, wherein a
material-permeable composite material is introduced into a
container having at least two openings.
81. The process as claimed in claim 80, wherein the composite
material is introduced into folded or rolled form in the
container.
82. The process as claimed in claim 38, wherein the composite
material is fixed in the container so that a gas flowing through
the filter has to pass through the composite material at least
once.
83. The process as claimed in claim 82, wherein the composite
material is fixed in he container be welding, soldering or adhesive
bonding.
84. The process as claimed in claim 38, wherein the support in the
composite material is connected to at least one power lead.
85. A process of cleaning waste or feed gases with the filter of
claim 1, comprising contacting the gases with the filter.
86. A process comprising cleaning waste gases from power stations
with the filter of claim 1, comprising containing the gases with
the filter.
87. A process of cleaning the exhaust gases of vehicles driven by
internal combustion engines with the filter of claim 1, comprising
contacting the gases with the filter.
88. A process of cleaning the exhaust gases of vehicles driven by
diesel engines with the filter of claim 1, comprising contacting
the gases with the filter.
89. A regenerable gas filter which comprises a bendable and
rollable composite material which is obtained by applying a
suspension which comprises at least one inorganic component
consisting essentially of a compound of at least one metal, a
semimetal or a mixed metal and at least one element of main groups
III to VII, and a sol to an open-structured and material-permeable
support to obtain an intermediate composite and subsequently
heating the intermediate composite at least once during which the
suspension comprising at least one inorganic component is
solidified in or on and in the support, wherein the composite
material has a thickness of 5 to 150 .mu.m and can be bent to a
radius of down to 2 mm, wherein the composite material has pores
permeable to particles having a maximum size of from 0.1 to 10
m.mu., and wherein there is present in the composite material at
least one inorganic component as a particle size fraction having a
particle size of 1 to 250 nm.
90. A regenerable gas filter according to claim 89 wherein the
suspension comprises A1.sub.2 O.sub.3, SiO.sub.2, TiO.sub.2 or
ZrO.sub.2 particles suspended in a sol obtained by hydrolyzing a
compound of Ti, Zr, Al, Sn, Ce or Y, and wherein the support
comprises metal or glass fibers.
91. A regenerable gas filter according to claim 90 wherein the
inorganic component is aluminum oxide having a particle size of 0.3
to 3 .mu.m.
92. A regenerable gas filter according to claim 90 wherein the
suspension comprises aluminum oxide suspended in a sol obtained by
hydrolyzing a zirconium compound.
93. A regenerable gas filter which comprises a composite material
which is obtained by application of a suspension in which the
suspension comprises at least one inorganic component consisting
essentially of a compound of at least one metal, a semimetal or a
mixed metal and at least one element of main groups III to VII in
at least one sol which is a metal oxide sol, semimetal oxide sol or
a mixed metal oxide sol to an open-structured and
material-permeable mesh support and subsequently heating at least
once during which the suspension comprising at least one inorganic
component is solidified in or on and in support, wherein the ratio
of the particle size of the suspended component to the mesh or pore
opening of the mesh support is from 1:1000 to 50:1000 and wherein
the composite material has a thickness of from 5 to 1000 .mu.m, and
wherein the mesh opening of the support is 50 to 500 .mu.m.
94. A regenerable gas filter according to claim 93, wherein at
least one catalytically active component is suspended in the
sol.
95. A regenerable gas filter which comprises a bendable or rollable
composite material which is obtained by applying a suspension of
aluminum oxide in a sol of hydrolyzed zirconium oxide to a
stainless steel mesh as a support to obtain an intermediate
composite and subsequently exposing the intermediate composite to
air at 450.degree. C. for 3 seconds, during which the said
suspension is solidified in or on and in the support.
96. A regenerable gas filter according to claim 95, wherein the sol
contains a suspended Pt/Rb catalyst.
Description
A gas filter, a process for producing a gas filter and use of this
gas filter are claimed.
Air pollution is known to present a serious problem in many parts
of the world. Depending on composition, the pollution can lead to
health problems among the human population. Furthermore, the air
pollution results in not inconsiderable economic loss. The air
pollution can be in the form of gases or of liquids dispersed very
finely in the air or in the form of tiny solid particles present in
the air. The solid particles which may be present in the air and
have been and are classified as carcinogenic include soot,
especially soot (particulates) which gets into the air via the
exhaust gases of diesel vehicles.
In many nations, regulations to regulate the maximum permissible
emission of particulates from motor vehicles have been put in
force.
Various methods and apparatus have already been developed for
treating solids-containing gases.
U.S. Pat. Nos. 4,972,889 and 4,948,403 claim ceramic filter system
which are able to filter soot or solid particles from the exhaust
gases of diesel-powered vehicles.
A problem with these methods and apparatus is that the solid
particles block the filter relatively quickly and the filters thus
have to be replaced or regenerated at short intervals.
To regenerate blocked filters, there have been proposals for
methods which burn the solids blocking the pores of the filter in
motor vehicles by additional combustion of fuel. The disadvantage
of these methods is that regeneration leads to an increased fuel
consumption. In addition, the deep action of this method is only
weak, so that blockages caused by particles in the filter cannot be
remedied.
More recently, methods and apparatus which remove filtered-out
solids from the filter by heating to 600.degree. C. have been
developed.
According to DE 3800723, additional heating wires are used for
heating the filter.
EP 0275372 uses heating elements comprising wire, expanded metal or
perforated foils for heating the filter.
GB 2193656 teaches a method and an apparatus which make use of
wires between which a current flows when a conductive bridge of
deposited soot forms.
U.S. Pat. No. 5,202,548 describes a filter which can be baked out
by application of a voltage since it is equipped with electrically
conductive honeycomb structures. U.S. Pat. No. 5,246,672 teaches
the use of woven wire meshes and U.S. Pat. No. 5,254,840 teaches
the use of a combination of metallic and ceramic honeycombs.
The filter materials used in the abovementioned methods or
apparatus have relatively small surface areas and thus either a low
filter action or, when the pores are made smaller to increase the
filter action, a small gas throughput. If the surface area is large
due to the use of porous materials, the pores become blocked very
quickly. Filtering relatively large amounts of gas requires the use
of large, relatively cumbersome gas filters which restricts the
possible uses of such gas filters.
It is therefore an object of the present invention to find an
economical process for producing a gas filter which, despite a
small size, is able to filter large amounts of gas and which can be
regenerated in a simple manner.
It has surprisingly been found that a gas filter which comprises a
material-permeable composite material based on at least one
open-structured and material-permeable support and having on at
least one side of the support and in the interior of the support at
least one inorganic component which comprises essentially at least
one compound of a metal, a semimetal or a mixed metal with at least
one element of main groups III to VII is able, even when small in
size, to filter large amounts of gas and can be regenerated in a
simple manner.
The present invention accordingly provides a regenerable gas filter
for filtering gases which comprises a composite material based on
at least one open-structured and material-permeable support and
having on at least one side of the support and in the interior of
the support at least one inorganic component which comprises
essentially at least one compound of a metal, a semimetal or a
mixed metal with at least one element of main groups III to
VII.
The present invention likewise provides a reaenerable gas filter
which comprises a composite material which is obtainable by
application of a suspension which comprises at least one inorganic
component comprising a compound of at least one metal, a semimetal
or a mixed metal with at least one element of main groups III to
VII and a sol to an open-structured and material-permeable support
and by subsequent heating at least once during which the suspension
comprising at least one inorganic component is solidified on or in
or on and in the support.
The present invention also provides a process for producing a gas
filter as claimed in any of claims 1 to 40, which comprises
producing a material-permeable composite material by applying, in
and on at least one open-structured and material-permeable support,
at least one suspension which comprises at least one inorganic
component comprising at least one compound of at least one metal, a
semimetal or a mixed metal with at least one of the elements of
main groups III to VII and a sol and by solidifying the suspension
on or in or on and in the support material by subsequent heating at
least once.
The present invention likewise provides for the use of a gas filter
as claimed in any of claims 1 to 40 for cleaning waste or feed
gases.
For the purposes of the present invention, material-permeable means
that materials which have this property are permeable to at least a
gas, a liquid or a solid. The permeability is dependent on the size
of the pores, mesh openings or holes which these materials
have.
The gas filter of the invention can be used for the filtration of
an,; waste and feed gases from Which, for example, solid particle
are to be removed. The gases to be filtered can also comprise vapor
or droplets of liquid. The advantage of the gas filter of the
invention is that, as a result of the use of an electrically
conductive support material in the composite material, the latter
can be baked out in a simple manner by application of a voltage and
thus be regenerated. If the composite material comprises
catalytically active materials, this heating only has to be carried
out once if the decomposition of the thermally decomposable liquid
droplets or solid particles is, in the case of a sufficiently hot
filter, catalyzed by the catalytically active materials and thus
proceeds swiftly. As a result, advantageously, a virtually constant
amount of gas can pass through the filter since blocking of the
filter by materials which are not thermally decomposable increases
only very slowly.
A further advantage of the gas filter of the invention is that the
novel composite material or gas filter can, due to the fact that it
is bendable, be rolled or folded and the filter-active surface area
of the filter can be very large in a small volume.
The gas filter of the invention is described below by way of
example without being restricted thereby.
The regenerable gas filter of the invention for the filtration of
gases comprises at least one composite material based on at least
one open-structured and material-permeable support and having on at
least one surface of the support and in the interior of the support
at least one inorganic component which comprises essentially at
least one compound of a metal, a semimetal or a mixed metal with at
least one element of main groups III to VII. For the purposes of
the present invention, interior of a support means, for example,
hollow spaces or pores in a support. According to the invention,
the regenerable gas filter comprises a composite material ,-which
is obtained by application of a suspension which comprises at least
one inorganic component comprising a compound of at least one
metal, a semimetal or a mixed metal with at least one element of
main groups III to VII and a sol to an open-structured and
material-permeable support and by heating at least once during
which the suspension comprising at least one inorganic component is
solidified on or in or else on and in the support.
According to the invention, the composite material or gas filter
can be permeable to gases, solids or liquids, in particular to
particles having a size of from 1.5 nm to 10 .mu.m.
A support having intermediate spaces having a size of from 50 to
500 .mu.m can advantageously be present in the composite material
of the gas filter. This support can comprise woven or felted
fibers, expanded metal or sintered metal. The support preferably
comprises at least one at least partially electrically conductive
material.
The intermediate spaces can be pores, mesh openings, holes, crystal
lattice interstices or voids. The support can comprise at least one
material selected from the group consisting of carbon, metals,
alloys, glass, ceramics, minerals, plastics, amorphous substances,
natural products, composite materials or at least one combination
of these materials. The supports which can comprise the
abovementioned materials can have been modified by a chemical,
thermal or mechanical treatment method or a combination of
treatment methods. Preferably, the composite material comprises a
support comprising at least one metal, a natural fiber or a plastic
which has been modified by at least one mechanical forming
technique or treatment method, e.g. drazing, swaging, fulling,
rolling, stretching or forging. Very particularly preferably, the
composite material comprises at least one support comprising at
least woven, bonded, felted or ceramically bound fibers or at least
sintered or bonded shaped bodies, spheres or particles. In a
further, preferred embodiment, a perforated support can be used.
Material-permeable supports can also be ones which become or have
been made material-permeable by laser treatment or ion beam
treatment.
It can be advantageous for the support to comprise fibers of at
least one material selected from the group consisting of carbon,
metals, alloys, ceramics, glass, minerals, plastics, amorphous
substances, composite materials and natural products or fibers of
at least one combination of these materials, e.g. asbestos, glass
fibers, rock wool fibers, carbon fibers, metal wires, steel wires,
polyamide fibers, coconut fibers or coated fibers. Preference is
given to using supports which comprise at least woven fibers of
metal or alloys. Wires can also serve as metal fibers. The
composite material very particularly preferably comprises a support
comprising at least one woven mesh of steel or stainless steel,
e.g. woven meshes produced from steel wires, steel fibers,
stainless steel wires or stainless steel fibers by weaving, which
preferably has a mesh opening of from 5 to 500 .mu.m, particularly
preferably mesh openings of from 50 to 500 .mu.m and very
particularly preferably mesh openings of from 70 to 120 .mu.m.
The support of the composite material can, however, also comprise
at least one expanded metal having a pore size of from 5 to 500
.mu.m. According to the invention, the support can also comprise at
least one granular, sintered metal, a sintered glass or a metal
nonwoven having a pore width of from 0.1 .mu.m to 500 .mu.m,
preferably from 3 to 60 .mu.m.
According to the invention, the composite material comprises a
support comprising at least aluminum, silicon, cobalt, manganese,
zinc, vanadium, molybdenum, indium, lead, bismuth, silver, gold,
nickel, copper, iron, titanium, platinum, stainless steel, steel,
brass, an alloy of these materials or a material coated with Au,
Ag, Pb, Ti, Ni, Cr, Pt, Pd, Rh, Ru and/or Ti.
The inorganic component present in the composite material or gas
filter can comprise at least one compound of at least one metal,
semimetal or mixed metal with at least one element of main groups
III to VII of the Periodic Table or at least one mixture of these
compounds. Here, the compounds of the metals, semi-metals or mixed
metals can comprise at least elements of the transition series and
main groups III to V or at least elements of the transition series
or main groups III to V, with these compounds having a particle
size of from 0.001 to 25 .mu.m. The inorganic component preferably
comprises at least one compound of an element of main groups III to
VIII or at least one element of main groups III to V with at least
one of the elements Te, Se, S, O, Sb, As, P, N, Ge, Si, C, Ga, Al
or B or at least one compound of an element of main groups III to
VIII and at least one element of main groups III to V with at least
one of the elements Te, Se, S, O, Sb, As, P, N, Ge, Si, C, Ga, Al
or B or a mixture of these compounds. Particularly preferably, the
inorganic component comprises at least one compound of at least one
of the elements Sc, Y, Ti, Zr, V, Nb, Cr, Mo, W. Mn, Fe, Co, B, Al,
Ga, In, Tl, Si, Ge, Sn, Pb, Sb or Bi with at least one of the
elements Te, Se, S, O, Sb, As, P, N, C, Si, Ge or Ga, e.g.
TiO.sub.2, Al.sub.2 O.sub.3, SiO.sub.2, ZrO.sub.2, Y.sub.2 O.sub.3,
BC, SiC, Fe.sub.3 O.sub.4, SiN, SiP, nitrides, sulfates,
phosphides, silicides, spinels or yttrium-aluminum garnet or one of
these abovementioned elements itself. The inorganic component can
also comprise alumino-silicates, aluminum phosphates, zeolites or
partially exchanged zeolites such as ZSM-5, Na-ZSM-5 or Fe-ZSM-5 or
amorphous microporous mixed oxides which may contain up to 20% of
non-hydrolyzable organic compounds, e.g. vanadium oxide-silicon
oxide glass or aluminum oxide-silicon oxide-methylsilicon
sesquioxide glasses.
Preferably, at least one inorganic component is present as a
particle size fraction having a particle size of from 1 to 250 nm
or having a particle size of from 260 to 10,000 nm.
It can be advantageous for the composite material to comprise at
least two particle size fractions of at least one inorganic
component. The particle size ratio of the particle size fractions
in the composite material is from 1:1 to 1:10,000, preferably from
1:1 to 1:100. The composite material particularly preferably
comprises at least one particle size fraction having an average
particle size of from 0.3 to 3 .mu.m. The ratio of the amounts of
the particle size fractions in the composite material is preferably
from 0.01:1 to 1:0.01.
The material permeability of the composite material can be limited
to particles having a particular maximum size by means of the
particle size of the inorganic component used. It can be
advantageous for the composite material to have pores which are
permeable to particles having a maximum size of from 0.1 to 10
.mu.m, particularly preferably a maximum size of from 0.2 to 1.5
.mu.m.
The suspension which comprises at least one inorganic component and
by means of which the composite material of the invention can be
obtained can comprise at least one liquid selected from the group
consisting of water, alcohol and acid or a combination of these
liquids.
In a further particular embodiment of the gas filter of the
invention, the composite material comprises at least one
catalytically active component. The catalytically active component
can be identical to the inorganic component. This applies
particularly when the inorganic component has catalytically active
centers on the surface.
The catalytically active component present in the composite
material is preferably at least one inorganic material, at least
one metal or at least one organo-metallic compound which has
catalytically active centers on its surface. The catalytic
component present in the composite material is particularly
preferably a zeolite such as ZSM-5, Fe-ZSM-5, silicalite or an
amorphous microporous mixed oxide as described, for example, in DE
195 45 0442 and/or DE 195 06 843, e.g. vanadium oxide-silicon oxide
glass or aluminum oxide-silicon oxide-methylsilicon sesquioxide
glasses.
The composite material can, however, also comprise at least one
oxide of at least one of the elements Mo, Sn, Zn, V, Mn, Fe, Co,
Ni, As, Sb, Pb, Bi, Ru, Re, Cr, W, Nb, Hf, La, Ce, Gd, Ga, In, Tl,
Ag, Cu, Li, K, Na, Be, Mg, Ca, Sr and Ba as catalytically active
component.
In a particular embodiment of the material-permeable composite
material, this comprises at least titanium suboxide as
catalytically active component.
It can likewise be advantageous for the composite material to
comprise, as catalytically active component, at least one metal
compound selected from among the compounds of the metals Pt, Rh,
Ru, Ir, Au, Ag, Os, Re, Cu, Ni, Pd and Co, or at least one metal
selected from among the metals Pt, Rh, Ru, Ir, Au, Ag, Os, Re, Cu,
Ni, Pd and Co.
Particularly preferred catalytic components are, for example, noble
metals, noble metal compounds or materials coated with noble metal
particles. The addition of the catalytically active component makes
it possible to achieve a situation where the filter becomes blocked
more slowly after heating once due to catalytic decomposition of
thermally decomposable solids or liquids, since only particles
which cannot be destroyed thermally block the filter. This
particular embodiment enables the operating life of the filter of
the invention to be increased considerably.
In a particularly preferred embodiment of the gas filter or
composite material of the invention, this can be made bendable
without destruction of the inorganic component solidified in the
interior of the support and on the support. The composite material
of the invention is able to be bent to a smallest radius down to 2
mm and preferably down to 1 mm.
Preferably, the composite material in the gas filter is rolled or
folded in a suitable container having at least one gas inlet and at
least one gas outlet, with the composite material being arranged so
that the gas to be filtered has to pass, after entering the gas
filter, at least once through the composite material before it can
leave the gas filter via the gas outlet.
In one variant of the gas filter of the invention, thermally
decomposable or sublimable or vaporizable solids or liquids which
have been filtered from a filtered gas and block the pores of the
composite material, e.g. soot or hydrocarbon particles, can be
removed from the gas filter by baking out the gas filter by
application of a voltage to the support of the composite material.
Depending on the selected support material, preferably a support
material having a low electrical resistance, the filter can be
heated using a low voltage as is customary, for example, in motor
vehicles, e.g. 12 or 24 V.
It can be advantageous for the gas inlet and the gas outlet to be
provided with a flow- or pressure-measuring device by means of
which the pressure or the amount of the gas entering and leaving
the filter is measured and for the heating of the gas filter to be
commenced on reaching a preset difference between the measured
values, which represents a measure of the blocking of the composite
material.
The process of the invention for producing the gas filter of the
invention is described below, without being restricted thereto.
The gas filter of the invention can be produced by producing a
material-permeable composite material by applying, in and/or on at
least one open-structured and material-permeable support, at least
one suspension which comprises at least one inorganic component
comprising at least one compound of at least one metal, a semimetal
or a mixed metal with at least one of the elements of main groups
III to VII and a sol and by solidifying the suspension on or in or
on and in the support material by subsequent heating at least
once.
When carrying out the process of the invention, it can be
advantageous to apply the suspension on and in or else on or in at
least one support by printing, pressing-on, pressing-in,
rolling-on, doctor blade coating, painting-on, dipping, spraying or
casting.
The open-structured and material-permeable support can comprise a
material selected from the group consisting of carbon, metals,
alloys, ceramics, glass, minerals, plastics, amorphous substances,
natural products, composite materials or at least one combination
of these materials. The preferred support is a woven stainless
steel or steel mesh.
The suspension used, which comprises at least one inorganic
component and at least one metal oxide sol, at least one semimetal
oxide sol or at least one mixed metal oxide sol or a mixture of
these sols, can be produced by suspending at least one inorganic
component in at least one of these sols. It can be advantageous for
the suspension to comprise at least one catalytically active
component. The catalytically active component can be identical to
the inorganic component.
The sols are obtained by hydrolyzing at least one metal compound,
at least one semimetal compound or at least one mixed metal
compound using a liquid, a gas or a solid. It can be advantageous
for the liquid used for hydrolyzing the compound to be hydrolyzed
to be water, alcohol or an acid or a combination of these liquids
or the solid used to be ice -or the gas used to be water vapor. It
can likewise be advantageous for the compound to be hydrolyzed to
be added prior to the hydrolysis to at least one alcohol or at
least one acid or a combination of these liquids. As compound to be
hydrolyzed, preference is given to hydrolyzina at least one metal
nitrate, a metal chloride, a metal carbonate, a metal alkoxide
compound or at least one semimetal alkoxide compound, particularly
preferably at least one metal alkoxide compound, a metal nitrate, a
metal chloride, a metal carbonate or at least one semimetal
alkoxide compound selected from among the compounds of the elements
Ti, Zr, Al, Si, Sn, Ce and Y or the lanthanides and actinides, e.g.
zirconium alkoxide, silicon alkoxide or titanium alkoxide
compounds, e.g. titanium isopropoxide, silicon alkoxides, zirconium
alkoxides, or a metal nitrate such as zirconium nitrate.
It can be advantageous to carry out the hydrolysis of the compounds
to be hydrolyzed using at least half the molar ratio of water,
water vapor or ice, based on the hydrolyzable group, of the
hydrolyzable compound.
The hydrolyzed compound can be peptized by treatment with at least
one organic or inorganic acid, preferably a 10-60% strength organic
or inorganic acid, particularly preferably a mineral acid selected
from the group consisting of sulfuric acid, hydrochloric acid,
perchloric acid, phosphoric acid and nitric acid and mixtures of
these acids.
It is possible to use not only sols which have been prepared as
described above but also commercial sols such as titanium nitrate
sol, zirconium nitrate sol or silica sol.
It can be advantageous if at least one inorganic component having a
particle size of from 1 to 10,000 nm is suspended in at least one
sol. Preferably, an inorganic component comprising at least one
compound selected from among metal compounds, semimetal compounds,
mixed metal compounds and metal mixed compounds with at least one
of the elements of main groups III to VI, or at least one mixture
of these compounds, is suspended. Particularly preferably, at least
one inorganic component comprising at least one compound selected
from among the oxides of the transition elements or the elements of
main groups III to V, preferably oxides selected from among the
oxides of the elements Sc, Y, Ti, Zr, Nb, Ce, V, Cr, Mo, W, Mn, Fe,
Co, B, Al, In, Tl, Si, Ge, Sn, Pb and Bi, for example Y.sub.2
O.sub.3, ZrO.sub.2, Fe.sub.2 O.sub.3, Fe.sub.3 O.sub.4, SiO.sub.2,
Al.sub.2 O.sub.3, is suspended.
The proportion by mass of the suspended component is preferably
from 0.1 to 500 times that of the hydrolyzed compound used.
In a particular variant, the sol used is preferably titanium
dioxide sol acidified with mineral acid and/or the inorganic
component used is preferable aluminum oxide having a particle size
of from 0.3 to 3 .mu.m.
It can be advantageous for at least one catalytically active
component, e.g. a noble metal or a noble metal compound, to be
added to the sol and to be incorporated into the gas filter or the
composite material.
It an likewise be advantageous for at least one catalytically
active component having a particle size of from 1 to 10,000 nm to
be suspended in a sol. Preferably, at least one catalytically
active component comprising at least one compound selected from
among metal compounds, semimetal compounds, mixed metal compounds
and metal mixed compounds with at least one of the elements of main
groups III to VII or organic compounds, or at least one mixture of
these compounds, is suspended. Particularly preferably, at least
one catalytically active component comprising at least one compound
selected from among aluminosilicates, aluminum phosphates, zeolites
or partially exchanged zeolites, e.g. ZSM-5, Na-ZSM-5 or Fe-ZSM-5,
and amorphous microporous mixed oxides which may contain up to 20%
of non-hydrolyzable organic compounds, e.g. vanadium oxide-silicon
oxide glass or aluminum oxide-silicon oxide-methylsilicon
sesquioxide glasses, is suspended.
The proportion by mass of the suspended components is preferably
from 0.1 to 500 times that of the hydrolyzed compound used.
Appropriate selection of the particle size of the suspended
compounds as a function of the size of the pores, holes or
intermediate spaces of the open-structured material-permeable
support, but also the layer thickness of the composite material of
the invention and the sol-solvent-metal oxide ratio, enable the
freedom from cracks of the gas filter of the invention or the
composite material to be optimized.
When using a woven mesh having a mesh opening of, for example, 100
.mu.m, it is possible to increase the freedom from cracks by using,
preferably, suspensions which comprise a suspended compound having
a particle size of at least 0.7 .mu.m. In general, the ratio of
particle size to mesh opening or pore size should be from 1:1000 to
50:1000. The composite material of the invention preferably has a
thickness of from 5 to 1000 .mu.m, particularly preferably from 50
to 150 .mu.m. The suspension comprising sol and compounds to be
suspended preferably has a weight ratio of sol to compounds to be
suspended of from 0.1:100 to 100:0.1, preferable from 0.1:10 to
10:0.1.
According to the invention, the suspension present on or in or else
on and in the support can be solidified by heating the composite at
from 50 to 1000.degree. C. In a particular variant, the composite
is subjected to a temperature of from 50 to 100.degree. C. for from
10 minutes to 5 hours. In a further particular variant, the
composite is subjected to a temperature of from 100 to 800.degree.
C. for from 1 second to 10 minutes.
The composite can be heated by means of heated air, hot air,
infrared radiation, microwave radiation or electrically generated
heat. In a particular embodiment of the process of the invention,
it can be advantageous for heating to be carried out using the
support material as electric resistance heating element. For this
purpose, the support can be connected via at least two contacts to
a power source. Depending on the power of the power source, the
voltage which is applied and the intrinsic resistance of the
electrically conductive support, the support heats up when the
power is switched on and the suspension present in and on the
support can be solidified thereby.
In a further, preferred embodiment of the process of the invention,
solidification of the suspension can be achieved by the suspension
being applied on or in or else on and in a preheated support and
thus being solidified directly after application. In a further,
particular embodiment of the process of the invention, it can be
advantageous for at least one support to be unwound from a roll,
passed at a speed of from 1 m/h to 1 m/s through at least one
apparatus which applies the suspension on or in or on and in the
support and at least one further apparatus which makes possible the
solidification of the suspension on or in or on and in the support
by heating and the composite material thus produced is wound up on
a second roll. This makes it possible to produce the gas filter of
the invention or the composite material by a continuous
process.
In a further, particular embodiment of the process of the invention
it can be advantageous to apply a ceramic or inorganic layer to a
support which may be a composite material or a composite material
produced by the process of the invention. This can be carried out,
for example, by laminating a green (unsintered) ceramic layer or an
inorganic layer which is, for example, present on an auxiliary film
onto the support or by treating the composite material with a
further suspension as described above. This composite can be
strengthened by heating, e.g. by means of infrared radiation or a
furnace.
The green ceramic layer used preferably comprises nanocrystalline
powder of at least one semimetal oxide or metal oxide such as
aluminum oxide, titanium dioxide or zirconium dioxide. The green
layer can also comprise an organic binder.
The use of a green ceramic layer males it readily possible to
provide the composite material of the invention with an additional
ceramic layer which, depending on the size of the nanocrystalline
powder used, restricts the material permeability of the composite
material produced in this way to very small particles.
The green layer preferably comprises nanocrystalline powder having
a particle size of from 1 to 1000 nm. If nanocrystalline powder
having particle sizes of from 1 to 10 nm is used, the composite
material of the invention to which an additional ceramic layer has
been applied has a material permeability four particles having a
size which corresponds to that of the particle size of the powder
used. If nanocrystalline powder having a size above 10 nm is used,
the ceramic layer is permeable to particles which are half the size
of the particles of the nanocrystalline powder used.
The application according to the invention of at least one further
inorganic layer or ceramic layer gives a composite material of the
invention which has a pore gradient. In addition, multiple
application of a layer makes it possible to produce composite
materials having a particular pore size using even those supports
whose pore size or mesh opening is not suitable for producing a gas
filter or composite material having the required pore size. This
may be the case, for example, when a gas filter or composite
material having a pore size of 0.25 .mu.m is to be produced using a
support having a mesh opening of above 300 .mu.m. To obtain such a
gas filter or composite material, it can be advantageous to first
apply to the support at least one suspension which is suitable for
treating supports having a mesh opening of 300 .mu.m and to
solidify this suspension after application. The composite material
obtained in this way can then be used as a support having a lower
mesh opening or pore size. It is possible to apply to this support,
for example, a further suspension which comprises, for example, a
compound having a particle size of 0.5 .mu.m.
The crack insensitivity of composite materials having large mesh
openings or pore sizes can also be improved by applying suspensions
which comprise at least two suspended compounds to the support. As
compounds to be suspended, preference is given to using compounds
which have a particle size ratio of from 1:1 to 1:10, particularly
preferably from 1:1.5 to 1:2.5. The proportion by weight of the
particle size fraction having the smaller particle size should nit
exceed a pro portion of at most 50%, preferably 20% and very
particularly preferably 10%, of the total weight of the particle
size fractions used.
Despite the application of an additional ceramic layer or inorganic
layer, which may comprise catalytically active components, to the
support, the composite material of the invention can be
bendable.
The gas filter of the invention or the composite material can also
be produced by laying a support, which may, for example, be a
composite material or another suitable support material, onto a
second support which may consist of the same material as the first
support or a different material or of two supports having a
different material permeability or porosity. A spacer, a drainage
material or another material suitable for conducting away
materials, e.g. a composite fabric, can be laid between the two
support materials. The edges of the two supports are joined
together, for example by soldering, welding or adhesive bonding.
Adhesive bonding can be carried out using commercial adhesives or
adhesive tape. The suspension can be applied in the manner
described above to the composite support prepared in this way.
In a particularly preferred embodiment, the superposed supports
between which at least one spacer, a drainage material or the like
may be arranged can be rolled up before or after, preferably after,
the joining of the edges of the supports. The spacing between two
composite supports which become juxtaposed on rolling-up can be
influenced by use of thick or thin adhesive tapes for joining the
edges of the supports. A suspension as described above can be
applied to such rolled-up composite supports by, for example,
dipping into a suspension. The composite support can be freed of
excess suspension by means of compressed air after dipping. The
suspension applied to the composite support can be solidified as
described above. A gas filter or composite material produced in
this way can be used as gas filter in a rolled module.
In a further particular embodiment of the process of the invention,
the composite support mentioned can also be produced by unrolling
two supports and, if provided, at least one spacer from individual
rolls and then laying them on top of one another. The edges of the
supports can again be joined by soldering, welding, adhesive
bonding or by other suitable methods of joining flat bodies. The
suspension can then be applied to the composite support produced in
this way. The application of the suspension can be carried out, for
example, by spraying or painting the composite support with the
suspension or by conveying the composite support through a bath in
which the suspension is present. The applied suspension is
solidified by one of the abovementioned methods. The composite
material produced in this way can be wound onto a roll. A further
suspension of a further inorganic layer can be applied to and/or
introduced into such a material by repeated application and
solidification. The use of different suspensions enables the
material properties to be set as desired or according to the
intended use. Not only further suspensions but also unsintered
ceramic and/or inorganic layers which are obtainable by
laminating-on as described above can be applied to this composite
material. This embodiment of the process of the invention can be
carried out continuously or batchwise, preferably continuously. A
composite material produced in this way can be used as gas filter
in a flat module.
The support in the gas filter or composite material can, depending
on the support material used, be removed again so as to form a
ceramic material which no longer contains any support material. If
the support material used is, for example, a natural material such
as a cotton nonwoven, this can be removed from the composite
material by oxidation in a suitable reactor. If a metal, e.g. iron,
has been used as support material, this support can be dissolved
out of the composite material by treating the composite material
with acids, preferably with concentrated hydrochloric acid. If the
support material additionally comprised zeolite, flat zeolite
bodies can be produced in this way.
It can be advantageous to use the composite material as support for
the production of a gas filter or composite material according to
the invention.
In a particular embodiment of the process of the invention, it is
possible, after solidification of the suspension or ceramic or
inorganic layer on and/or in the support material, to treat the
dried and strengthened gas filter or composite material with a
solution comprising at least one metal compound, preferably a metal
salt such as RhCl.sub.3. The treatment can comprise, for example,
spraying, painting or rolling the solution comprising a metal
compound onto the composite material or, for example, dipping the
composite material into a solution comprising a metal compound. The
gas filter or composite material which has been treated in this way
is dried by heating. Heating can be carried out as indicated above.
The metal compound which is present in and on or in or on the
composite material after application and drying of the solution is
reduced to the metal.
It can be advantageous to reduce a metal compound present in and/or
on the composite material to the metal using a reducing agent,
preferably a borohydride, very particularly preferably NaBEt.sub.3
H, LiBEt.sub.3 H, NaBMe.sub.3 H or KBPr.sub.3 H.
It can likewise be advantageous to reduce a metal compound present
on or in or else on and in the composite material to the metal by
using the composite material as electrode in an electrolysis.
Catalytically active metals can also be applied in and/or on the
gas filter or composite material by using a composite material
without a catalytically active component as electrode in the
electrolysis of a solution comprising a noble metal salt. Here, it
is necessary for the composite material to comprise at least
TiO.sub.2 as an inorganic component and at least one partially
electrically conductive support. On application of a voltage of,
for example, from 2 to 3 volt, the composite material becomes
electrically conductive due to formation of titanium suboxide,
which is electrically conductive. As a result of the electrolysis,
catalytically active noble metal, preferably in the form of very
fine particles, deposits in and/or on the composite material or gas
filter.
This makes it possible to produce gas filters which comprise metals
and/or noble metals as catalytic components.
It is also possible to use the gas filter or composite material of
the invention as support for producing a gas filter according to
the invention.
In a particular variant for producing the gas filter of the
invention, at least one material-permeable composite material is
introduced, preferably rolled or folded, into a container having at
least two openings.
The composite material is preferably fixed in the container,
preferably by welding, soldering or adhesive bonding, so-that a gas
flowing through the filter has to pass through the composite
material at least once. The support in the composite material of
the gas filter is preferably connected to at least one power
lead.
It can be advantageous to combine preferred embodiments of the
process of the invention with at least one further preferred
embodiment of the process of the invention. It may likewise be
advantageous to combine preferred embodiments of the. gas filter of
the invention with at least one further preferred embodiment of the
gas filter of the invention. With knowledge of the present
invention, a person skilled in the art will be able to see further
embodiments of the process of the invention, the gas filter of the
invention and/or further possible uses of the process of the
invention or the gas filter of the invention.
The gas filter of the invention can be used for cleaning gases, in
particular waste gases or feed gases, and very particularly
preferably gases containing at least one solid.
The gas filters of the invention are preferably used for cleaning
waste gases from power stations or for cleaning the exhaust gases
from vehicles driven by internal combustion engines. The gas filter
of the invention is very particularly preferably used for cleaning
the exhaust gases from vehicles driven by diesel engines.
The following examples describe the process of the invention for
producing a gas filter according to the invention, without the
process being restricted to these examples.
EXAMPLE 1
A suspension comprising 25 g of zirconium isopropoxide was
hydrolyzed with 20 g of water. The resulting precipitate was
subsequently treated with about 40 g of 25% strength nitric acid
and, after the precipitate had dissolved completely, 60 g of
aluminum oxide (A16SG from Alcoa) were added. This suspension was
stirred until all agglomerates had completely dissolved and ;as
applied in a thickness of 60 .mu.m to a square-weave mesh of
stainless steel having a mesh opening of 70 .mu.m. This composite
was exposed to air at 450.degree. C. for 3 seconds and was dried
and solidified in this way.
The composite material obtained in this way was used `for gas
filtration. The present composite material is suitable, when
installed in a gas filter, for filtering exhaust gases from diesel
engines, since solid particles having a size of upward from 0.25
.mu.m are selectively retained.
The solid particles having a size of greater than 0.25 .mu.m which
are filtered out gradually block the filter during use. Application
of a voltage to the support of the composite material enables the
filter or the composite material to be heated so that particles
able to be destroyed thermally can be removed from the filter by
means of oxidation reactions.
EXAMPLE 2
A Pt/Rh catalyst is incorporated on and in a composite material as
produced and described in Example 1. For this purpose, a suspension
comprising a zirconium oxide sol which had been prepared by
hydrolyzing 25 g of zirconium isopropoxide with 20 g of water and
subsequently treating the resulting precipitate Edith 40 g of 25%
strength nitric acid and container the Pt/Rh catalyst in a
concentration of 1% was applied on and in the composite material as
support. Solidification of the suspension by heating the composite
by means of air at 450.degree. C. for 3 seconds gave a composite
material which is suitable for use as or in a gas filter.
This gas filter, too, is very useful for the filtration of gases
containing solid particles. The solid particles having a size of
greater than 0.25 .mu.m which are filtered out gradually block the
filter during use. Application of a voltage to the support of the
composite material enables the filter or the composite material to
be heated so that particles able to be destroyed thermally can be
removed from the filter.
When the filter has reached a suitable process temperature at which
the oxidatively decomposable solids can be destroyed catalytically
by oxidation reactions owing to the presence of the Pt/Rh catalyst,
the solids which have been filtered out are continually destroyed
by oxidation, resulting in considerably reduced blockage of the gas
filter. In this embodiment of the gas filter of the invention,
energy does not have to be consumed continually for regeneration of
the filter, but it is sufficient for the gas filter to be heated at
least once during the start-up or running-up phase. Once the
reaction in and on the filter is proceeding, the energy liberated
in the destruction of the solid particles generates the high
temperatures necessary for regeneration of the filter.
* * * * *